A microwave communication device generally transmits and receives a signal simultaneously using different frequencies. This frequency utilization manner causes a waste of frequency spectrum resources. Therefore, a full-duplex communication technology, that is, a frequency spectrum utilization manner where data transmitting and data receiving are performed simultaneously on the same frequency spectrum, is proposed. This can greatly improve frequency spectrum utilization efficiency.
A critical problem in full-duplex communication is that, because a device performs transmitting and receiving on the same frequency, a transmit antenna of the device causes intra-frequency interference to a local receive antenna, and the intra-frequency interference cannot be suppressed by using a filter. Therefore, it is a critical problem to be solved to increase isolation between transmit and receive antennas of the device for implementing full-duplex communication.
At present, the following two existing technologies are available to solve the intra-frequency interference problem between transmit and receive antennas of a device in the full-duplex communication technology.
FIG. 1 and FIG. 2 illustrate a technical solution using three antennas in the prior art. As shown in FIG. 1, the technical solution uses two transmit antennas TX1 and TX2, and one receive antenna RX. A difference in a distance between the two transmit antennas and the receive antenna is λ/2, where λ is a carrier wavelength. A signal transmitted by the transmit antennas TX1 and TX2 is received by the receive antenna RX, resulting in intra-frequency interference.
In this solution, a transmitted signal is split by a power splitter into two identical signals which are respectively fed into the transmit antennas TX1 and TX2. Because a difference in the distance to the position of the receive antenna is λ/2, a difference in a phase of the two transmitted signals arriving at the receive antenna is 180°, and therefore interference of the two signals are offset against each other.
In this technical solution, one of the transmit antennas is used to generate an offsetting signal to offset interference of the other transmit antenna on the receive antenna.
On the basis of this technical solution, the two transmit antennas are replaced with receive antennas, and the receive antenna is replaced with a transmit antenna. In this case, the power splitter functions to combine power to obtain an antenna system of “two receivers and one transmitter” (two receive antennas and one transmit antenna). The principle thereof is the same as the technical solution in the literature, as shown in FIG. 2.
The solutions illustrated in FIG. 1 and FIG. 2 use an assistance antenna to generate an interference offsetting signal, which increases the number of antennas.
Another existing technical solution is to increase a distance between transmit and receive antennas. An increased distance between antennas may increase a free space loss of interference, so as to increase the isolation between the transmit and receive antennas. However, the increased distance between antennas results in a larger size of the overall antenna system.